At present, many terminals equipped with a large-capacity storage battery may be used as power supply terminals to charge other terminals. When a power supply terminal is connected to a power receiving terminal through a USB (Universal Serial Bus, universal serial bus) port, the following charging solution may be used to charge the power receiving terminal:
The power supply terminal short-circuits two data pins D+ and D− of the USB port, and charges the power receiving terminal by simulating a standard charger. When a charging capability of the power supply terminal can meet a requirement of the power receiving terminal, that is, when a maximum charging current that can be output by the power supply terminal is not less than a charging current required by the power receiving terminal, the power supply terminal can charge the power receiving terminal. However, when the charging capability of the power supply terminal cannot meet a requirement of the power receiving terminal, that is, when a maximum charging current that can be output by the power supply terminal is less than a charging current required by the power receiving terminal, a voltage at the USB port of the power supply terminal drops, which may eventually lead to a charging failure.
It can be seen that compatibility of the foregoing solution is relatively poor. In many cases, a power supply terminal cannot use the foregoing solution to charge a power receiving terminal.